(1) Field of the Invention
The present invention relates to a patterning method for micro-contact printing which makes it possible to form micro-contact printed patterns with a size as large as a molecule used in the production of a variety of functional molecular devices and a DNA chip and printed product obtained by this method.
(2)Description of the Prior Art
In the field of molecular chemistry, L. Carter proposed the concept of a molecular device in 1982. Research and development in this field has been actively carried out in enterprise, university and research institutes since that time. For example, if a specific function is given to each organic molecule, respectively and an assembly of these organic molecules is formed, the assembly of organic molecules makes possible the formation of a semiconductor device with a super-high integrated density such that there is no comparison between the integrated density of a semiconductor device formed of the assembly of organic molecules and that of a conventional semiconductor device. Further, in recent years, the genome analysis of DNA has been actively studied and the so-called biochip has attracted the attention of people. The application thereof is also thought for the development of the biochip.
On the other hand, in photolithography employed until now as a method of reproducing micro-contact printed patterns, there is a limit for the reproduction of micro-contact printed patterns in respect of mass-production of micro-contact printed patterns being made in a short time since a substrate with desired micro-contact printed patterns should be reproduced through several steps. Further, photolithography is not suited for materials with a low heat resistance and low mechanical resistance such as cells, DNA and enzymes, since photolithography is carried out through complicated steps such as exposure, development and etching. Further, printing method makes possible the production of massive printed products. However, the reproduction of micro-contact printed patterns of the order of hundreds μm is the limit until now. Accordingly, a printing method is not suited for the reproduction of micro-contact printed patterns.
Inventors of the present invention previously invented a method of reproducing micro-contact printed patterns comprising the steps of: forming patterns of molecules with a polarity on a substrate using molecular ink including molecules with a fixed polarity dispersed in a solvent to form a first transfer layer and forming patterns of molecules with the same polarity as the above-mentioned polarity or a different polarity from the above-mentioned polarity on the substrate using molecular ink including molecules with the same polarity as the above-mentioned polarity or the different polarity from the above-mentioned polarity (Japanese patent application No. 2000-151157).
However, in the above-mentioned method, the density of the ink used is lowered for increasing the resolving power. The film of the first transfer layer has defects since the first transfer layer is transferred using an ink with a thin density. When the second transfer layer is formed, the ink for the second transfer layer comes in and contaminates the first transfer layer formed previously because an area of the first transfer layer is not covered completely with ink for the first transfer layer, so that the contrast between the first transfer layer and the second transfer layer is lowered.
Further, there is a problem that if the density of the ink for the first transfer layer is increased in order to remove defects of the first transfer layer in forming the first transfer layer, the running and spreading of ink occurs so that the resolving power is lowered.